Question

I’m using the latest versions of MongoDB (on a Win 64 Server) and the C# driver. I have a windows service that is doing 800 reads and updates per minute, and after a few minutes the current threads used goes above 200 and then every single mongodb call gives this error:

System.IO.IOException: Unable to read data from the transport connection: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond. ---> System.Net.Sockets.SocketException: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond
   at System.Net.Sockets.Socket.Receive(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags)
   at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)

I have an index on the fields that is reading by so that’s not the issue. Here is the code for the read:

public static UserUpdateMongo Find(int userId, long deviceId)
{
    return Collection().Find(
        Query.And(
            Query.EQ("UserId", userId),
            Query.EQ("DeviceId", deviceId))).FirstOrDefault();
}

I instantiate the connection like so:

var settings = new MongoServerSettings
{
    Server = new MongoServerAddress(segments[0], Convert.ToInt32(segments[1])),MaxConnectionPoolSize = 1000};
    Server = MongoServer.Create(settings);
}

Am I doing something wrong or is there an issue with the C# driver? Help!!

Answer 1

The C# driver has a connection pool, and the maximum size of the connection pool is 100 by default. So you should never see more than 100 connections to mongod from a single C# client process. The 1.1 version of the C# driver did have an occasional problem under heavy load, where an error on one connection could result in a storm of disconnects and connects. You would be able to tell if that was happening to you by looking at the server logs, where a log entry is written every time a connection is opened or closed. If so, can you try the 1.2 C# driver that was released this week?

You should not have needed to create a queue of pending updates. The connection pool acts as a queue of sorts by limiting the number of concurrent requests.

Let me know if you can find anything in the server logs, and if there is anything further I can help you with.